1. Field of the Invention
This invention relates generally to a hydrostatic axial piston machine having a swashplate construction with a cylinder block in which there are a plurality of bores with pistons that can move longitudinally in the bores. The pistons are each supported by a slipper on a swashplate, with the slippers connected with the pistons by a slipper joint, in particular by a ball joint.
2. Technical Considerations
Axial piston machines of the above type are known in numerous embodiments in the known art. A distinction between machines is thereby made by the type of cylinder block bearing system, i.e., an internal bearing system and an external bearing system for the cylinder block. With a conventional internal bearing system, the cylinder block is mounted on a rotating shaft that is supported in the machine housing by roller bearings. The cylinder block is driven by a shaft gearing which makes possible both axial mobility of the cylinder block and a limited angular adjustability. The position of the cylinder block can thereby be adapted to the position of the port plate. The cylinder block is supported on the shaft at the intersection of the plane containing the center points of the slipper joints with the axis of rotation of the cylinder block or the axis of rotation of the shaft. In known axial piston machines, this intersection lies axially outside the cylinder block (i.e., axially between the cylinder block and the swashplate). Therefore, on axial piston machines that have a cylinder block with an internal bearing system, the cylinder block is elongated toward the swashplate by a throat. On axial piston machines with a cylinder block that has an external bearing system, instead of the throat there is a collar on the outer periphery of the cylinder block. The measures described above (throat or collar on the cylinder block) result in a certain minimum length of the axial piston machine.
DE 34 23 467 C2 discloses an axial piston machine in which the intersection of the plane of the center points of the slipper joints with the axis of rotation of the cylinder block also lies outside the cylinder block, although the cylinder block has neither a throat nor a collar. These components are not necessary because a conical bearing, namely an angular ball bearing, a conical roller bearing, or a friction bearing, is used as the cylinder block bearing system. This type of cylinder block bearing system can be used both for the external bearing system and for the internal bearing system of the cylinder block. On this known axial piston machine, however, one disadvantage is that when the cylinder block becomes worn in the vicinity of the port plate and wear plate, there is no possibility for a readjustment of the cylinder block in the axial direction, which is limited by the conicity of the cylinder block bearing.
Therefore, it would be advantageous to provide a compact hydrostatic axial piston machine of the type described above that can be used in many different applications and has an improved cylinder block bearing system.
The invention provides an axial piston machine in which the center points of the slipper joints are located in a plane, the intersection of which plane with the axis of rotation of the cylinder block is located in an end surface of the cylinder block that contains the piston exit openings or in an area of the cylinder block that is adjacent to this end surface. Because the invention teaches that the above mentioned intersection point is located axially inside the actual cylinder drum or on its swashplate-side outer periphery, the support of the cylinder block requires neither special components that are axially connected to the cylinder block and determine its length, nor conical bearings that restrict the freedom of movement of the cylinder block (adjustability). On the other hand, the cylinder block, in contrast to the indirect bearing systems of the prior art, can be supported directly in the area of the axial extension of the bores (friction bearings or roller bearings that are realized in the form of radial bearings). The axial piston machine of the invention can thereby be made very short in the axial direction.
The cylinder block is preferably supported by bearings in the area of the intersection of the plane of the center points of the slipper joints with the axis of rotation of the cylinder block.
In one particularly advantageous refinement of the invention, the center points of all the slipper joints are located inside the axial extension of the bores in the cylinder block. The transverse piston forces, in contrast to the swashplate motors of the prior art, are thereby not applied to the free ends of the piston, but are absorbed inside the axial extension of the bores in the cylinder block. Consequently, the pistons are no longer subjected to bending loads and can thereby be made significantly shorter, which has advantages with regard to the size of the axial piston machine. The guided length of the pistons in the bores of the cylinder block can be reduced with respect to the dimensions of systems of the prior art (corresponding to approximately 1.5 to 2.5 times the piston diameter) to a dimension that is sufficient to seal the bores. The dimension in the axial direction of the axial piston machine of the invention is therefore very small in relation to the displacement.
Finally, the mass of the pistons is also significantly reduced over that of conventional axial piston machines. The inertial forces are therefore also reduced. These reductions are reflected, for example, in a reduction of the load on the piston retraction device during operation of the axial piston machine of the invention in the form of a self-priming pump. The centrifugal forces generated during the rotation of the cylinder block are also reduced.
There are several possible methods to locate the center points of all the slipper joints inside the axial length of the bores in the cylinder block. For example, the maximum angle of adjustment of the swashplate can be reduced so that all the pistons are inserted all the way into the bores. By means of increased piston diameters and correspondingly enlarged intake cross sections, in this case it is at least partly possible to compensate for a reduction in the discharge or intake capacity of the axial piston machine of the invention. The result is a short-stroke machine which has the advantage of a low piston velocity.
In an additional configuration of the invention, the slipper joints are located in the pistons and each piston joint is connected with the corresponding slipper by a connecting rod. With an appropriate length of the connecting rods, it becomes possible to achieve a full insertion of the pistons into the corresponding bores with an unchanged large adjustment angle of the swashplate.
To prevent an increase in the weight of the slipper systems resulting from the presence of the connecting rods, or to at least partly compensate for such an increase, the invention teaches that it is advantageous if the slippers and/or the connecting rods and/or the slipper joints are made at least partly from a light metal alloy. Under some conditions, however, an increase in the weight of the slipper system can be acceptable if the slippers are combined with the short and therefore lightweight pistons described above.
The axial piston machine of the invention can be realized both in the form of a cylinder block with an internal bearing system and also in the form of a cylinder block with an external bearing system. If the cylinder block has an external bearing system, there are advantages with regard to the input/output of the cylinder block. In such a case, the cylinder block can be connected, instead of with a shaft that has to transmit both torsion forces as well as bending loads, with a centrally located torque rod. Such a torque rod, which is free of transverse forces, can have a diameter which is significantly smaller than the input/output shaft described above.
The cylinder block may be provided with a bearing system that permits an axial movement of the cylinder block, in particular a system of roller bearings. However, it is also possible to provide a system of friction bearings.
In one advantageous embodiment of the invention, a housing is provided with a housing base, whereby the housing base has a closable recess. A passage to another machine can be created through the recess.
It is also possible to locate an additional machine, in particular an auxiliary pump, in the recess of the housing floor. The additional machine is thereby integrated into the axial piston machine without increasing the outside dimensions of the axial piston machine.
In an additional embodiment of the invention, a gear train on the swash-plate side is coupled with the axial piston machine. In this manner, the speed of rotation of the axial piston machine can be increased and decreased.
If the gear train is realized in the form of a single-stage planetary gear train that has a sun wheel coupled with a transmission shaft and a ring gear coupled with the torque rod, the result on one hand is compact dimensions. On the other hand, when the axial piston machine of the invention is used as a pump, for example, the speed can be reduced to reduce noise and vibrations (e.g., ratio 2:1 for a single-stage planetary gear train, if the ring gear has twice the diameter of the sun wheel).
On the other hand, the additional machine can be operated with its speed of rotation unchanged, if the machine is coupled to the sun wheel of the planetary gear train and/or of the transmission shaft. It is also possible, however, to operate the axial piston machine and the additional machine at the same speed of rotation, e.g., by coupling the additional machine with the cylinder block and/or the torque rod.
In many applications, for example when the axial piston machine of the invention is used as a pump driven by an internal combustion engine of a hydrostatic traction drive system, the invention teaches that it is advantageous, with regard to noise reduction, if the torque rod is connected to the cylinder block with the interposition of a damping device.